Industrial and automotive applications such as motor current sensing and battery voltage monitoring require precise measurement of the current or voltage level. Offset voltage present in a sensor chip used for precision current or voltage measurement will appear in the measurement reading and hence requires one-time calibration at the system level to remove this offset from the measurement. Offset voltage of a sensor chip is defined as the output voltage when the input signal is zero, in other words the condition when the input signal is connected to ground.
One-time offset calibration is performed by first connecting the input of the sensor chip to ground to measure the offset voltage at the output, and then subtracting this offset voltage from subsequent readings when the sensor is in normal operation. For practical reasons, calibration is performed only one time at nominal operating conditions. Hence, only a fixed offset is eliminated and so this scheme is only accurate for measurement done at the calibration conditions.
As offset changes over the device operating conditions such as temperature and supply voltage, and also varies from part to part due to manufacturing process shift, this calibration scheme is not effective to cancel offset due to drifts in operating environment. This calibration has to be performed for every sensor chip at the system level